Building OMS is not that difficult, the difficult part is the setups. So first you need to code your setup, entry and exit triggers and charting the way you like it, eg what time frame, or if multiple time frame than accordingly make charts. Also there will be different setups or strategies for different market conditions or market structures. So you have may have 2 -3 or 4 etc setups. This you can invoke at the click of a mouse or on the buttons on charts. e.g. Strategry 1, Strategy 2 etc. So once you have "decided" which strategy you think is suiting the particular day then you can click on that button and then your system will give you entry / exit alerts etc. This can then be executed through OMS.
The other point which is important is MM, so first define this part and link it with historic volatility in the market. So you calculations of position is automatically done as per 'historic' volatility (not future, because we do not know anything in future). So when you run OMS you are not bothered about position size and your MM is taken care of. This I think is paramount to trading success.
Then the last part is analytics, what you have done (actual trade) has to be recorded for analysis. Like what zerodha shows in quant. Here you can create anything you want. Like I have a candlestick chart of my P&L. It is like any any chart of nifty or stock. Has high lows, close. The high shows my profit which went till that level (though I did not book it) and the lows shows my loss which went till that leve (though I did not book it). Every trade is one candle, every day P&L is one candle, every week too. So seeing this chart too gives a net idea of how well my own Stock is doing and when to take pause or actively participate in markets. So this is one thing. Similarly on day type basis you can have data, what happens on Monday, on Friday, on expiry day. Long or short what is best for you. etc etc. The list is long.
Because it is possible to code all what you need and suits your trading behaviour you can benefit. To conclude what will suit me may or may not suit you.
Hope this helps.